In measurements of distance between two points, a very important advance has been made by using electromagnetic waves. The distance can be calculated if the measured time of the waves spreading from the transmitter to the reflector is multiplied by the known velocity of the waves.
The purpose of the universal reflector according to the invention is that it can be applied for the measurements of hydraulic parameters in rivers and other water currents, especially for streamlines and trajectories. Further, for the measurements of water velocity, sea-level altitude of the water surface according to the principle of placing the instrument which generates and emits electromagnetic waves (transmitter) and at the same time receives the reflected waves (receiver) in one point.
The range of the classical optics is a very small part of the whole spectrum of electromagnetic radiation, the visible part of the spectrum being between 4000 .ANG.n and 7500 .ANG.n (.ANG.ngstrom).
Electromagnetic telemeters applied in this range are known as electro-optical telemeters. Among the most efficient available electro-optical instruments are the laser telemeters because of their special possibilities of scope, accuracy, and efficiency.
The most important advantage of the laser beam is its monochromity and coherence. These characteristics of laser beams mean that the laser light waves are co-ordinated in time and space. The monochromity of the laser light is 250.times.10.sup.6 and the stability of frequency is 10.sup.7 times superior to the monochromity of ordinary light.
In the group of electro-optical and laser telemeters, simple plane mirrors or prisms have been applied as reflectors up to now. However, such reflectors have to be carefully oriented normally to the direction of the incoming electro-optical beam in order to reflect the incoming beam to the instrument (receiver).
When measuring the distance to an immobile object whict can be reached, the orientation of the mirror or the prism normally to the direction of the measuring distance has been performed by standard treatment known in physics and geodesy.
When measuring a moving object (e.g., a float in a water stream), its position must be determined in another way, since the demanded hydraulic parameters are defined by its movement. The float thrown into the water stream and carried by the water flow describes the trajectory (geometrical locus of points through which a part of a fluid passes on its way through the space), by the line of consecutive positions, that is the streamline (the line which refers to a definite moment in time and at each point has a tangent in the direction of the velocity at that point). Both lines, the trajectory and the streamline have tangents in the direction of the velocity, but the tangents of the trajectory refer to the velocity of the same part in different moments, and the tangents of the streamlines refer to the simultaneous velocities of different parts. The trajectories and the streamlines are the same in fixed (i.e., stable) currents.
Since a float is mobile and can not be reached, its position has been determined by means of two theodolites cutting the direction at the same moment. This has been done by measuring the horizontal connecting angles--the method known in geodesy as "cutting forward". The position of the float in horizontal projection (that is, only with x, y co-ordinates) has been determined. The horizontal projection of the streamline (trajectory) has been obtained on the map or plan by connecting the series of such consecutive points.
The simultaneity of measuring the horizontal angles is obtained by using visual-optical or auditory signals or by taking the readings at determined time intervals. In any case, the "forced measurement" was always performed by one theodolite not when it was favourable, but when it had to be done. The transmission of these signals from one to the other instrument needed numerous personnel to perform the measurements, and an accumulation of inevitably delay occurred which lead to considerable error in determining the horizontal position of the float. The accuracy of determining the float position by this method is about .+-.50 cm, according to some lacking data in the references and some author's analysis.
Electro-optical instruments have been made in combination with theodolites in recent years, and they operate together with the telescope of theodolites so that distance and both vertical and horizontal angles can be measured at the same time. Next to the reflector which reflects electromagnetic impulses there has to be a sightmark in which the sighting is performed by the optical axis of the teodolite. The distance between the electro-optical beam and the optical axis of the theodolite is constant for the determined combination.
Many new eletro-optical instruments (especially laser telemeters) have their own limbs (horizontal and vertical), and it is possible to place the laser beam in the direction of the optical axis of the theodolite telescope. That is, the laser beam has in a way materialized the optical axis of the theodolite. In the situation like this, sighting into the reflector is at the same time sighting into the sight point of the optical system in order to measure the horizontal and vertical angles.
Very simple floats which float on the water surface have been constructed for measurements by floats. One of the simple floats is a cross-float made of two boards put crosswise. In the middle of such a float a holder is mounted with a sight-mark on it.
Other kinds of floats have been used, including one made of a round wooden board with a weight hanging on it to make the float stable. On the upper part of the board, which is above the water level, the sight-mark is mounted.
Other floats are of cylindrical shape with the bases of cone shape. A weight is hung on the lower basis, and the lower basis and the sight-mark are mounted on the upper basis.
All of the foregoing kinds of floats are imperfect. They are unstable in the water, the wind and water waves can easily turn or overturn them, and the direct distance from the float and the instrument can not be measured by them.
Some trilateral prisms are known (triple prisms, cube prisms, retrodirected prisms) which have been used for measurements with electro-optical and laser telemeters, especially when a quick measurement of detailed points on the terrain has been performed, and the surveyor's assistant should not pay attention to his orientation towards the instrument. These prisms reflect the light beam to .+-.20.degree. angle of incidence to the main normal.
The technical problem solved or ameliorated by the subject invention is how to measure the distance by electro-optical and laser telemeter to a moving object which during its movement takes arbitrary positions which are not foreseen or determined. Specifically, the subject invention permits, by means of a telemeter, the measuring of the surface and deep streamlines and trajectories in open water currents, rivers, seas and lakes, and the measuring by means of a telemeter of the water velocity and the sea-level altitude of the water surface through a reflector from which the emitted electromagnetic wave or beam is reflected back to the source of emission--the receiver.